A5080413205- Graphene research and applications
- 2D Materials and Applications
- Quantum and electron transport phenomena
- Perovskite Materials and Applications
- Semiconductor Quantum Structures and Devices
- MXene and MAX Phase Materials
- Topological Materials and Phenomena
- Physics of Superconductivity and Magnetism
- Plasmonic and Surface Plasmon Research
- Nanowire Synthesis and Applications
- Quantum optics and atomic interactions
- Advancements in Semiconductor Devices and Circuit Design
- Molecular Junctions and Nanostructures
- Carbon Nanotubes in Composites
- Quantum Dots Synthesis And Properties
- Quantum Information and Cryptography
- Quantum, superfluid, helium dynamics
- Photonic Crystals and Applications
- Electronic and Structural Properties of Oxides
- Iron-based superconductors research
- Surface and Thin Film Phenomena
- Metamaterials and Metasurfaces Applications
- Strong Light-Matter Interactions
- Thermal Radiation and Cooling Technologies
- ZnO doping and properties
Universidade Federal do Ceará
2016-2025
University of Antwerp
2010-2025
Columbia University
2015-2018
Universidade de Brasília
1999
Universidade Federal de Minas Gerais
1995
Abstract The ability to control the size of electronic bandgap is an integral part solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning energies states based on unusual strength Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering surrounding dielectric environment, one can tune exciton binding energy monolayers WS 2 WSe hundreds meV. We exploit this behaviour present in-plane heterostructure...
Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Though highly desirable, a comprehensive characterization still lacking. Here we report systematic study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers photon energy spanning 0.25 1.36 eV. Each exhibits thickness-dependent unique spectrum...
The Dirac equation is solved for triangular and hexagonal graphene quantum dots different boundary conditions in the presence of a perpendicular magnetic field. We analyze influence dot size its geometry on their energy spectrum. A comparison between results obtained with zigzag armchair edges, as well infinite-mass condition, presented our show that type edge choice appropriate have very important single-particle levels are calculated function an external field lifts degeneracies. Comparing...
External fields are a powerful tool to probe optical excitations in material. The linear energy shift of an excitation magnetic field is quantified by its effective g-factor. Here we show how exciton g-factors and their sign can be determined converged first principles calculations. We apply the method monolayer excitons semiconducting transition metal dichalcogenides interlayer MoSe$_2$/WSe$_2$ heterobilayers obtain good agreement with recent experimental data. precision our allows assign...
We calculate the excitonic spectrum of few-layer black phosphorus by direct diagonalization effective mass Hamiltonian in presence an applied in-plane electric field. The strong attractive interaction between electrons and holes this system allows one to investigate Stark effect up very high ionizing fields, including also excited states. Our results show that band anisotropy becomes evident direction dependent field induced polarizability exciton.
We determine the strongly layer-dependent exciton binding energies in few-layer black phosphorus by infrared spectroscopy.
The time evolution of a wavepacket in strained graphene is studied within the tight-binding model and continuum model. effect an external magnetic field, as well strain-induced pseudo-magnetic on wave packet trajectories zitterbewegung are analyzed. Combining effects strain with those field produces effective which large one Dirac cones, but can be practically zero other. We construct efficient valley filter, where for propagating incoming consisting momenta around K K' points, outgoing...
We review the transmission properties of carriers interacting with potential barriers in graphene. The tunneling electrons and holes quantum structures graphene is found to display features that are marked contrast those other systems. In particular, interaction between electrostatic can be related propagation electromagnetic waves media negative refraction indices, also known as metamaterials. This behavior becomes evident one calculates time evolution wavepackets propagating across barrier...
An analytical approach, using the Dirac-Weyl equation, is implemented to obtain energy spectrum and optical absorption of a circular graphene quantum dot in presence an external magnetic field. Results are obtained for infinite-massand zigzag boundary conditions. We found that with condition exhibits zero-energy band regardless value field, while infinite-mass condition, states appear only high fields. The results compared those from tight-binding model: (i) we show validity range continuum...
We report the experimental observation of radiative recombination from Rydberg excitons in a two-dimensional semiconductor, monolayer WSe2, encapsulated hexagonal boron nitride. Excitonic emission up to 4s excited state is directly observed photoluminescence spectroscopy an out-of-plane magnetic field 31 T. confirm progressively larger exciton size for higher energy states through diamagnetic shift measurements. This also enables us estimate 1s binding be about 170 meV, which significantly...
Hyperbolic polaritons exhibit large photonic density of states and can be collimated in certain propagation directions. The majority hyperbolic are sustained man-made metamaterials. However, natural-occurring materials also exist. Particularly, natural in-plane layered have been demonstrated MoO3 WTe2, which based on phonon plasmon resonances respectively. Here, by determining the anisotropic optical conductivity (dielectric function) through spectroscopy, we predict that monolayer black...
Abstract Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to defect traps and strong exciton-exciton interaction in TMDs has significantly limited efficiency of emission from this class materials. Here, we show 1L-WS 2 effectively screened using an ultra-flat Au film substrate separated by multilayers...
Within a minimal model, we present analytical expressions for the eigenstates and eigenvalues of carriers confined in quantum rings monolayer bilayer graphene. The calculations were performed context continuum model by solving Dirac equation zero width ring geometry, i.e., freezing out carrier radial motion. We include effect an external magnetic field show appearance Aharonov-Bohm oscillations nonzero gap spectrum. Our gives insight on energy spectrum graphene-based models different aspects...
We present a systematic study of the energy spectra graphene quantum rings having different geometries and edge types in presence perpendicular magnetic field. Results are obtained within tight-binding (TB) Dirac models we discuss which features former can be recovered by using approximations imposed latter. Energy levels diagonalizing TB Hamiltonian demonstrated to strongly dependent on geometry microscopical structure edges. This makes it difficult recover those existing theories that...
Propagation of an electron wave packet through a quantum point contact (QPC) defined by electrostatic gates in bilayer graphene is investigated. The provide bias between the layers, order to produce energy gap. If on both sides same bias, steps transmission probability are observed, as usual QPC. However, if inverted one QPC, only electrons belonging Dirac valleys allowed pass, which provides very efficient valley filtering.
Mechanical deformations and ensuing strain are routinely exploited to tune the band gap energy enhance functionalities of two-dimensional crystals. In this Letter, we show that leads also a strong modification exciton magnetic moment in WS_{2} monolayers. Zeeman-splitting measurements under fields up 28.5 T were performed on single, one-layer-thick microbubbles. The bubbles causes hybridization k-space direct indirect excitons resulting sizable decrease modulus g factor ground-state exciton....
We describe a semianalytic approach to the two-band Ginzburg-Landau theory, which predicts behavior of vortices in superconductors. show that character short-range vortex-vortex interaction is determined by sign normal domain-superconductor interface energy, analogy with conventional differentiation between type I and II However, we also long-range modified parameter ${\ensuremath{\kappa}}^{*}$, different from standard $\ensuremath{\kappa}$ bulk superconductor. This opens possibility for...
The effect of an external in-plane electric field on neutral and charged exciton states in two-dimensional (2D) materials is theoretically investigated. These are argued to be strongly bound, so that electron-hole dissociation not observed up high intensities. Trions the anisotropic case monolayer phosphorene demonstrated especially robust under fields, fields as 100 kV/cm yield no significant trion binding energy or probability density distribution. Polarizabilities excitons obtained from...
Trions and biexcitons in anisotropic two-dimensional materials are investigated within an effective mass theory. Explicit results obtained for phosphorene arsenene, that share features such as a direct quasiparticle gap conduction valence bands. predicted to have remarkably high binding energies elongated electron-hole structure with preference alignment along the armchair direction, where masses lower. We find biexciton also notably large, especially monolayer phosphorene, they found be...
The vortex-vortex interaction potential in bulk superconductors is calculated within the Ginzburg-Landau (GL) theory and obtained from a numerical solution of set two coupled non-linear GL differential equations for vector superconducting order parameter, where merger vortices into giant vortex allowed. Further, potentials between an antivortex are both type-I type-II superconductors. Our results agree asymptotically with analytical expressions large inter-vortex separations which available...